Here's an idea I'm kicking around.
What makes you do things every day? (as opposed to one-time things)
- Needs: if something is not right in your life, you will have an incentive to change things.
- Habits: it's what you always do.
- Nothing else.
Habits are obvious. I don't have citations handy, but I'm pretty sure we live most of our lives habitually.
Needs are sort of rare and have to be pretty severe. If I practiced two languages, drawing, working-memory, strength/coordination training, and another bit of meditation for 10 minutes each day, I'd probably be a superhero, for only the cost of an hour each day. But I don't, because there's no need. I've only been able to start doing a couple things, really, and meditation is the biggest, and it took a relatively large crisis of "what is my mind and what am I doing with my life."
Tim Ferriss (and Malcolm Gladwell?) talks about this as "the Harajuku moment" (he knew a guy who, while sitting in fashionable Harajuku, Tokyo, realized "no matter what clothes I buy, I'll always look like hell", and then immediately started to get into shape intensely and successfully). BJ Fogg's behavior model talks about motivation, ability, and triggers. We're talking about things you have the ability to do (sleep more, eat this and not that) so motivation is the biggest issue. But I think I'm disagreeing with him on the types of motivation: I think senses and social issues aren't part of it.
Maybe this is going in circles. I'm pretty sure it's not saying something new; needs more polish. But the point is, I think there are not many reasons to make a behavior change.